My goal is to find a treatment for stroke and CNS injury. Such injuries are partly mediated by synaptic glutamate receptors, which are also essential for CNS function. Curtailing synaptic function with glutamate antagonists is harmful and is a failed approach to treating stroke in humans. We have shown that toxic glutamatergic signals are restricted to distinct pathways, indicating that they might be blocked selectively, without affecting essential synaptic activity. This grant pursues our discovery of the molecular mechanism for neurotoxic signaling, which depends on NMDA receptor (NMDAR) interactions with submembrane scaffolding proteins. A key interaction is that of NMDARs with the scaffolding protein PSD-95. We have suppressed neuronal PSD-95, which uncoupled NMDARs from nitric oxide synthase, an enzyme tethered to NMDARs by PSD-95. This blocked NMDAR toxicity without blocking synaptic activity. More recently, using cell-permeant peptides that disrupt NMDAR/PSD-95 coupling, we treated stroke in animals. The treatment reduced focal ischemic brain damage in rats and improved their neurological outcome without blocking synaptic function. Our approach avoids the negative consequences of blocking NMDARs and may constitute a practical stroke therapy. We propose to pursue this promising approach further. In AIM 1 we will determine the mechanism of action of the therapeutic molecules that we discovered. In AIM 2 we will focus on the therapeutic limits (therapeutic window, duration of effect, neurobehavioral consequences) and toxicity of treating stroke and CNS trauma by dissociating NMDAR/ PSD-95 interactions. In AIM 3 we will identify novel therapeutic targets for neurological disease based on downstream interactions of PSD-95. The results will provide knowledge on mechanisms of disease and synaptic function, and validate a stroke treatment with the future intention of proceeding to human trials.